linux-kernel - Re: revert "fs/befs/linuxvfs.c: replace strncpy by strlcpy"

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Message-ID: <CA+55aFwbRZe5gVsTyHvjKqE5eA3zQ_58_UQW7KACCt7V7FpZbQ@mail.gmail.com>
Date:	Tue, 28 Apr 2015 14:48:45 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Fabian Frederick <fabf@...net.be>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
Subject: Re: revert "fs/befs/linuxvfs.c: replace strncpy by strlcpy"

On Tue, Apr 28, 2015 at 2:38 PM, Chris Metcalf <cmetcalf@...hip.com> wrote:
>
> To do that we'd probably want to provide a generic version that
> just copied byte-by-byte, and encourage architecture variants
> that were more efficient.

Our generic "strncpy_from_user()" is actually fairly efficient, and
reasonably portable. It almost has to be, since this is actually a
much more common - and much more critical - load than any regular
strncpy I know of in the kernel.

I suspect you could take that lib/strncpy_from_user.c and massage it
reasonably trivially to be a good function.

That said, I can't think of a single strncpy (or strlcpy) in kernel
space that is actually worth even optimizing for. They just don't tend
to be in the critical path. So correctness is likely *much* more
important than worrying about performance.

                           Linus
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